The present invention relates to a process and an apparatus for the continuous production of slabstock foam, in which a liquid reaction mixture is fed, divided transversely and allowed to cream and foam, following which the expanded slabstock foam is then removed.
It is known for example to produce a liquid reaction mixture of polyol and isocyanate for the continuous production of polyurethane slabstock foam by feeding the liquid reaction mixture into a relatively large distributing trough for a certain residence time, a run-off plate whose angle of inclination can be adjusted being arranged behind the trough. As a result of this residence in the distributing trough, the upper region of the reaction mixture creams, flows as it were in the xe2x80x9crising jetxe2x80x9d onto and over the run-off plate and then foams to form a block (see DE-OS 2 142 450, believed to correspond to GB-PS 1 354 34). It has been found that this process and the associated apparatus are not suitable for processing rapidly reacting chemical systems since the mixture in the trough in this case quickly foams starting from the dead zones, i.e. the low-flow zones in the distributing trough. Complicated and expensive cleaning and paper lining procedures for the distributing trough are necessary before and after each foaming procedure.
According to another known process the liquid reaction mixture is usually applied from above to a trough-shaped paper film spread over a floor plate, the paper film being drawn, together with the applied and still liquid reaction mixture, underneath by an air gap. This air gap is formed by a guide roller underneath which runs a cover film (manufacturer""s logo xe2x80x9c51/1xe2x80x9d xe2x80x9cQFMxe2x80x9d of Hennecke GmbH, D-53754 Sankt Augustin, No. D 9901-820 362 3T 10/98 Go). Under the correct procedure the liquid reaction mixture forms a small bulge in front of this air gap, which prevents penetration of air between the reaction mixture and cover film. However, this does not prevent bubbles of air forming undesirable eddies in the reaction mixture when the latter is applied to the lower paper film. These bubbles are subsequently often the starting point for the formation of cavities.
There is thus a need to provide a process and apparatus by means of which slabstock foam can be produced without any restrictions a priori free of cavities, i.e. can be produced from rapidly reacting chemical systems.
This object is achieved if the reaction mixture discharges from underneath, in front of, and/or through a floor plate over which the reaction mixture is present substantially still in a liquid state, i.e. before the reaction mixture visibly foams. Normally three phases are distinguished during the reaction, namely the liquid phase, the creamy phase with a marked rise in viscosity on account of the (also visible) formation of foam, and the rising phase in which there is basically a build-up of the microfoam bubbles formed in the creamy phase. According to the invention the reaction mixture should have reached the floor plate before the onset of the creamy phase.
The time available from the discharge from the mixing device to the application to the floor plate is, according to the invention, about 1 to 10 seconds, preferably 1 to 5 seconds.
The new apparatus for the continuous production of slabstock foam from a liquid reaction mixture comprises a mixer together with an associated floor plate, a transporting system lined internally with films and provided with lateral boundaries being connected in the conveying direction behind the floor plate.
The novel feature of the invention is that the floor plate is arranged in each region in which the reaction mixture above this floor plate is substantially still liquid, and that the inlet for the liquid reaction mixture discharges from underneath, in front of, and/or through the floor plate.